Are heat and temperature the same?? Lets find out!

SOME BASIC FACTS TO START HEAT is a form of energy Heat is the energy of vibrating molecules THEREFORE all matter which is made of molecules has heat Remember the particle theory of matter again- how fast something vibrates determines how hot it is (you will need this for the test) WHERE DOES HEAT COME FROM??? The SUN is the largest source of energy It warms the earth and plants grow to help provide animals with food- and the animals and plants give us food Burning fuel can provide some heat as can: coal, oil, gas and wood But ALL these things needed the sun to form in the first place Rubbing or friction can produce heat- but most of this heat is not wanted…why??? (destroys the machinery by wearing things out). We can use oil or grease to eliminate this problem (its called lubricant)

THERMOMETERS These measure temperature- NOT heat Heat is a form of energy- it describes the total of all the energy of all the particles within an object. Temperature: In every day language we use the words heat and temperature interchangeably BUT they are DIFFERENT TEMPERATURE tells us how HOT or Cold SOMETHING is It depends on how quickly the particles are moving in the substance Hotter things have faster moving particles

Measuring Temperature Our skin measures temperature with receptors (remember back to body systems) A thermometer gives an accurate idea of how hot or cold something is It usually contains a liquid- either alcohol or mercury The liquid expands when heated and moves up the glass tube Temperature is measured in degrees Celsius (0C) Some times we use the Fahrenheit and Kelvin scales LETS LOOK AT PAGE101 TOGETHER

What things affect heat loss and gain?? Heat is transferred in various ways….coming up next BUT, the amount of heat that can be gained or lost by an object depends on three things: Its mass What it is made of The temperature change/difference

HEAT TRANSFER Heat flows from one object to another- from the hottest to the coldest The greater the temperature difference the faster the heat flows There are three main ways heat is transferred: Conduction Convection Radiation

CONDUCTION READ PAGE 102 TOGETHER (NOW basic notes) Hotter substances have particles jiggling faster than others If this was particles in a hot soup in a mug- they make the particles in the spoon jiggle faster too- the hot soup heats up the spoon This is because the particles pass their heat from one to another like a chain reaction this passing of heat from one particle to another is CONDUCTION

Conductors Conductors- “conduct” or easily pass on heat from one thing to another: metals are good conductors glass is better than polystyrene- metal is better again Insulators: If we want to protect ourselves from the heat….like a saucepan handle when cooking we use a material called an insulator: some good insulators are: plastic polystyrene air cloth wood rubber PRAC PAGE 109- TESTING INSULATORS/ comparing materials

CONVECTION WHEN AIR IS HEATED THE PARTICLES GAIN ENERGY AND CAN MOVE FURTHER APART Hot air (you may have heard this ) rises,….this is because it is less dense than cool air The cool air pushes it upwards This method of heat transfer is CONVECTION As the air flows around from cool to hot and so on, it is called a convection current Open fires work like this, the saucepan on the earlier slide is both conduction and convection….? Who can explain why?? Convection works for liquids and gases as their particles are already freely moving not like the particles in a solid

Convection currents- sun/earth and hot water systems Convection currents –PLEASE draw you need them for the test  (also see page 104 text book)

Other examples of convection: Tea leaves being boiled in water The heater /fire warming up the air in your living room Heating the water in a saucepan ? Do the exercise on page 104 convection currents Radiation When heat energy is transferred through a vacuum – its radiation The sun sending its heat through empty space to warm you while you sit in your deck chair at the beach is radiation The sun can’t send heat via convection/conduction as there are no particles in space

Radiation contd: Radiation of heat is by invisible waves that travel at the speed of light (300000km/second) Infrared radiation is heat energy transmitted this way All objects emit some infra-red radiation The hotter something is the more it radiates When radiated heat hits a surface it is absorbed, reflected or transmitted through it It may be partially absorbed, reflected or transmitted PLEASE DRAW THE DIAGRAM 4.1.15 PAGE 105

What affects radiation??? Dark colours heat up or absorb more quickly Light colours reflect heat/radiation Dark colours also lose heat quicker …that’s why the black cup of coffee cools quicker than the one with milk in it  Lighter colours lose heat slower. Shiny bright surfaces reflect the best/absorb the worst NOTE: microwaves use radiation- they heat food by having the waves bounce/reflect from the metal surface inside the microwave and be absorbed by the food…cooking it while the heat is then transferred to all the food in the dish by conduction Practical : ? PG 110 COMPARING HEAT RADIATION or page 160 Infrared radiation

Specific heat capacity??? What the ?? Every substance e.g water, milk etc has a specific heat capacity… That is a measure of how much energy we need to raise the temperature of 1 gram of that substance by 1 degree celcius Formula is: Q = Cm T answer is in joules (j) HEAT SPECIFIC MASS CHANGE IN HEAT TEMPERATURE CAPACITY

Examples….specific heat If you are told water has the specific heat capacity of 4.2 joules…. and I ask you how much heat is needed to heat a 30 mls of water form 40 degrees to 100 degrees….. HOW do you work that out?? 1ml = 1 gram Therefore Q = c x m x T Heat = 4.2 x 30 x 60 Heat = 126 x 60 Heat = 7560 joules T